1. Field of the Invention
The present invention relates generally to agricultural seeders that produce open furrows in the soil into which seeds are placed, and more particularly, to an improved furrow closing wheel for use with such seeders for closing a furrow in which seeds have been placed.
2. Description of the Prior Art
Agricultural planting methods continue to evolve in response to widespread adoption of crop production techniques with greatly reduced dependence on tillage of the soil (“no-till” or “reduced-till”), and in which the new crop's seeds are often placed directly into the previous crop's stubble or crop residues. No-till or reduced-till seeding differs greatly from seeding into a tilled seedbed. The soil conditions for no-till seeding are typically wetter than those dried by tillage, due to the mulching effect of the crop residue remaining on the soil surface. Wetter soils are more prone to compaction by implements traveling over or engaging the soil. No-till soils are also typically more structurally stable than tilled soils, as the soil particles are “aggregated” or held together by old roots, fungi, and other organic substances and molecular attractions binding the particles together. Agricultural seeders operating in no-till conditions are often equipped and adjusted to employ more down-pressure, either via coil spring or hydraulics, on the furrow opening blades to aid in the slicing of old crop residues and to assist in the penetration of this more structured soil. The extra down-pressure on the opener disc and depth-gauging wheel often results in more compaction of the furrow sidewall.
Especially in no-till or other wet conditions, some difficulties are encountered when attempting to draw soil back into the furrow, which is desirable to protect the newly placed seeds from drying winds and sun, to protect from, predation, to allow for proper seedling development, and to improve seedling uniformity of growth. In tilled soils, the prior art was to employ packing wheels rearward of the furrow openers. The packing wheels operated to both close the furrow and to do some amount of packing, since in the loose and dry conditions of tilled soils a considerable amount of packing is desirable to assist the seed in drawing moisture from below the seed.
In no-till seeding, the wetter and more structured soils generally prevent packing wheels from performing adequately. The sidewall of the furrow formed in no-till seeding does not crumble easily like the sidewall in the tilled conditions, where the soil had previously been loosened and fluffed by tillage. Accordingly, very high pressures are sometimes applied to the packing or closing wheels in an attempt to squeeze the furrow sidewalls back together. This typically results in poor seedling emergence because the soil in the furrow is more compressed at the surface compared to near the seed, even to the extent of having a void immediately above the seed but with extremely compressed soil at the surface. In this instance, seed germination may fail due to the drying of air in the void, or the seedling may leaf underground in the void, or the seedling will encounter great difficulty pushing itself through the dense layer of soil, which will slow and weaken the seedling or even kill it.
Some improvements have been made by separating the seed firming and furrow closing functions. This is typically only possible where the depth-gauging function is already accomplished independently of the packing or closing wheel, as in the configuration where depth-gauging wheels travel alongside the furrow opening discs. Seeds are firmed into the soil in the bottom of the furrow by a narrow rolling wheel or sliding-type firmer exerting a small amount of pressure onto the seed after it has been placed by the furrow openers and seed-directing tube. Since the closing wheel is now relieved of its packing function, the preferred method of closing furrows in no-till has diverged from smooth wheels toward spoked or tined wheels as being better suited to crumbling the more resilient sidewalls of the furrow that occur in no-till conditions.
Several spoked closing wheel types have been invented, as shown, for example, in U.S. Pat. No. 5,443,023 issued to Carroll, U.S. Pat. No. 5,497,717 issued to Martin, U.S. Pat. No. 5,896,932 issued to Bruns et al, and U.S. Pat. No. 5,970,891 issued to Schlagel. Experience has taught that the results vary widely depending on the exact geometry and configuration of the spokes on such a wheel, as well as the angles at which the spokes engage the soil.
Some spoke designs inherently do a great deal of packing of the soil above the seed, which is generally undesirable and was a major reason for the departure from smooth closing wheels. Certain other designs penetrate the soil all too well, and too deeply, and have a pronounced tendency to lift and ‘chunk up’ the sidewall and disrupt seed placement. Yet another problem of many prior art designs is the tendency to accumulate mud, corn stalks, corn cobs, or other debris, often to the extent of clogging the wheel and arresting its rotation, or to the lesser degree of filling the places between the spokes and eliminating the effectiveness of the wheel for furrow closing. Altering the angles at which the spokes engage the soil will alleviate some of the effects of sidewall lifting, such as taught by Hagny, U.S. Pat. No. 6,314,897, although the design of the spoked wheel itself remains a crucial component in obtaining good results in sidewall breakage and avoiding mud accumulation.
In particular, Schlagel and Carroll were designed to do considerable packing of the soil, and do in fact achieve this. This is obtained by relatively large surfaces of the spoke contacting the soil, and forcing this surface into the soil with a combination of weight and spring pressure. Carroll's spoke has a rather large flat area initially contacting the soil, the tine being 0.75-inch wide, and with a curvature and directionality such that a considerable surface on the side of the leading edge of the tine contacts and compresses the soil. In field operation, the portion of Carroll's tine initially engaging the soil and being forced into the soil is approximately an area exceeding 1.0 inch2. Carroll's design does a great deal of packing of the soil overlying the seed during its attempt to close the furrow, which was a stated purpose of the wheel, and no other seed firming device was contemplated by Carroll. Schlagel's design has still greater contact area, and is quite limited in its ability to penetrate the soil.
FIGS. 1 to 4 of Bruns depict spoked wheels with greatly reduced contact area, approximately 0.05 inch2, although Bruns' spokes of “truncated cone” shape possess a significant enlargement of these two dimensions moving toward the spoke base from this initially small contact area. Spoked wheels embodying the Bruns patent, such as the “Star” wheel marketed by May-Wes Mfg. of Hutchinson, Minn., do indeed enter the soil much more readily than the quite blunt spokes taught by Carroll. Bruns discloses a wheel used for “furrow closing” without mention of the wheel supplying any seed firming action, apparently assuming such firming function would be accomplished by other methods—indeed, the industry was well on its way to widespread use of separate in-furrow firming devices by the date of Bruns' invention.
Similarly, Martin teaches a spoked wheel with its closing function separate from the seed firming action, which Martin envisioned as being accomplished with a trailing press wheel centered on the midline of the furrow to pack the soil behind the closing wheels. Accordingly, the closing wheel in Martin has an exceptionally small contact area, essentially zero with its “sharpened” spokes, which allows the spokes to easily enter the soil. As both Bruns and Martin contemplate seed firming accomplished by other means, those patents refocused attention on spokes that readily enter the soil, rather than some compromised blend of intermittent packing/crumbling.
Other attributes that determine the ease with which the spokes enter the soil are the length and tapering of the spokes. These attributes also play a major role in the depth to which the spokes penetrate. While it is desirable for spoked closing wheels to penetrate the soil easily initially, and to achieve some depth to break apart the sidewall, it is highly undesirable that the spokes achieve too much depth and disrupt seed placement. The wheel in FIGS. 1 to 4 of Bruns features spokes that taper sufficiently in two directions to limit depth effectively. Conversely, Martin teaches a closing wheel with spokes having parallel sides (with sharpened ends) and a length of 2.5 inches—the stated goal being to till the furrow sidewall to the depth of seeding. Experience has shown that wheels per this design can penetrate too deeply and disrupt seed placement, contrary to the claims of Martin. Indeed, the spoke attributes of Martin's wheel are better suited to row cleaning ahead of the opener, rather than furrow closing, and the wheel depicted in Martin's U.S. Pat. No. 5,497,717 is changed little if any from the row cleaning wheel Martin describes in U.S. Pat. No. 4,785,890.
Furrow closing wheels preferably provide considerable shattering action of the upper portion of the furrow sidewall to allow root development, while creating a consistent amount of ‘fill’ over the seed without an overabundance of air pockets or large clods. Attributes of the spoked wheel design affect this, including the geometry and length of the spokes as previously described, and also the proximity of the spokes to each other along the wheel's periphery. Generally, closely spaced spokes break up the sidewall more. Longer radial spokes tend to penetrate more deeply and to create more lifting action upon exiting the soil—lifting is typically undesirable as it increases the likelihood of disrupting seed placement as well as reducing control over the movement of the broken pieces of sidewall, i.e., churning and flinging the sidewall chunks, instead of shoving them directly into the furrow.
Another factor in the performance of spoked closing wheels is the ability to avoid clogging or accumulation of mud, straw, stalks, cobs, vines, and other materials commonly found in no-till fields, for the reasons stated earlier. Some prior art designs have experienced major problems with accumulation of mud and debris. By way of example, Carroll's design is capable of accumulating mud and old crop residues to such an extent as to require a pair of covering plates, as described in U.S. Pat. No. 5,645,000. The May-Wes “Star” wheel has problems with mud accumulation also, Bruns' recitation of the non-stick qualities of UHMW notwithstanding. Martin tends to have somewhat less problems with mud accumulation, due to the large open spaces between its spokes.
Prior art spoked closing wheels also have a tendency to accumulate vines of certain weed or crop species. These vines are carried up and around the wheel by the spokes, sometimes falling in toward the axis of the wheel and becoming lodged thereon. Additional vine accumulation causes tighter wrapping around the wheel axle or spindle, creating friction between the wheel and its support bracket, eventually to the point of stopping the wheel's rotation.
Still more shortcomings of prior art closing wheels pertain to the mechanical bearings and bearing housings for rotation of the wheel. Prior art closing wheels typically have rather small lightweight bearings or pairs of bearings with at least one face of one bearing exposed, which creates problems with water, liquid fertilizers, and dust corroding and abrading the seals and races, and eventually compromising the integrity of the seal. Bearing seizure and failure soon follow.